The disclosures of Japanese patent Application Nos. 2001-96770 filed on Mar. 29, 2002 and 2002-22164 filed on Jan. 30, 2002, including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
1. Field of the Invention
The invention relates to an exhaust gas purifier for internal combustion engine.
2. Description of the Related Art
In the internal combustion engine, particularly in a diesel engine, particulates mainly composed of soot are contained in the exhaust gas. Since such particulates are harmful substance, it is proposed that a particulate filter for collecting the particulates before being discharged to the atmosphere is disposed in an exhaust system of the engine. However, in order to prevent the increase of exhaust gas resistance due to the clogging, the collected particulates should be combusted. In such filtering regeneration, the particulates may be ignited for the combustion at about 600xc2x0 C., but the exhaust gas temperature of the diesel engine is generally lower than 600xc2x0 C. and it is necessary for the filter itself to be heated.
According to Japanese Patent Application Laid-open No. 7-106290, it is disclosed that the particulates on the filter are continuously combusted at the temperature of about 400xc2x0 C. which is the normal temperature of the diesel engine exhaust gas by adding the platinum metal and alkaline-earth metals to the filter. However, even using such filter, it is not certain that the temperature of the exhaust gas is always maintained at 400xc2x0 C. and depending on the driving condition of the engine, a great amount of the particulates may be discharged from the diesel engine and accumulated gradually on the filter, which are not combusted at each timing.
When the particulates are accumulated to a certain amount on this filter, the combustion capacity for the particulates will be decreased not to regenerate the filter by itself Thus, it is not sufficient to provide simply such filter in the engine exhaust system. This may cause clogging at an early timing and may influence on the output performance of the engine.
It is an object of the invention to provide an exhaust gas purifier for an internal combustion engine, which can prevent an early clogging of a particulate filter and at the same time can decrease the discharge amount of the harmful substances contained in the exhaust gas to the atmosphere other than the particulates.
According to a first aspect of the invention, the exhaust gas purifier for the internal combustion engine includes a particulate filter disposed in the engine exhaust system for collecting the particulates and a reversing device that reverses an exhaust gas upstream side and an exhaust gas downstream side of the particulate filter. The collected particulates by the filter are oxidized and the filter includes a collecting wall for collecting the particulates. The collecting wall includes first and second collecting surfaces, which are alternately used for collecting the particulates by reversing the exhaust gas upstream side and downstream side of the filter by the reversing device. A catalyst device is provided adjacent to the particulate filter at the position of always keeping downstream side of the filter.
Some particulates may be left on the first collecting surface of the particulate filter collecting wall due to insufficient oxidization according to the driving condition. However, according to the first aspect of the exhaust gas purifier for the internal combustion engine, the reversing of the exhaust gas upstream side and downstream side by the reversing device will not let the particulates be accumulated on the first collecting surface of the collecting wall and a gradual oxidization removal of the particulates is possible. At the same time, by the second collecting surface of the collecting wall, the collection and oxidization of the particulates begin. By alternate using of the first and second collecting surfaces for particulates collection, the amount of the collected particulates at each collecting surface can be reduced compared to the collection by using a single collecting surface. This will be advantageous in oxidization removal of the particulates to obviate the accumulation of the particulates on the filter to eventually prevent clogging of the filter.
Further, since the catalyst device is provided always at the downstream of the particulate filter adjacent thereto, the catalyst device functions relatively effectively by the temperature increase through the heat conductivity from the particulate filter to reduce a possible large amount discharge of the harmful substances other than the particulates contained in the exhaust gas.
In the first aspect of the invention, the collecting wall may carry an active oxygen release agent to oxidize the particulates by active oxygen released from the active oxygen release agent.
In the above aspect, the active oxygen release agent captures and retains the surrounding excess oxygen and discharges the collected oxygen in the form of active oxygen when the surrounding oxygen concentration is decreased.
In the first aspect of the invention, the catalyst device can be structured to carry the oxidization catalyst.
In the first aspect of the invention, the catalyst device can be structured to carry the NOx catalyst.
In the first aspect of the invention, the reversing device may include a valve body, and the exhaust gas upstream side and downstream side of the particulate filter may be reversed by changing the position of the valve body from a first position to a second position, and the exhaust gas may flow into the catalyst device without passing through the particulate filter when the valve body is positioned at an intermediate position between the first and second positions.
In the above aspect of the invention, the valve body can be positioned at the intermediate position immediately after the engine starts.
In the above aspect of the invention, the exhaust gas purifier device may include a temperature detecting device that detects or assumes a temperature of the catalyst device, and when the temperature detected or assumed by this temperature detecting device is not within a predetermined temperature range, the valve body may be set to be the intermediate position for changing the exhaust gas condition to control the catalyst device temperature to be within the predetermined range.
In the above aspect of the invention, the exhaust throttle valve may be provided in the engine exhaust gas system, and the position of the valve body may be controlled at the intermediate position immediately before the exhaust throttle valve is opened.
In the above aspect of the invention, when the engine is under deceleration, the valve body may be positioned at the intermediate position, and at the same time the temperature of the exhaust gas may be increased or the deoxidization substances in the exhaust gas may be increased.
In the first aspect of the invention, the reversing device may include a valve body, and may reverse the exhaust gas upstream side and the exhaust gas downstream side of the particulate filter by switching the valve body from a first position to a second position, and the catalyst device may be arranged adjacent to a downstream of the valve body.
In the first aspect of the invention, the catalyst device may be arranged closer to the internal combustion engine than the particulate filter, and the catalyst device may be connected to the particulate filter so that the exhaust gas that flows out the particulate filter flows into the catalyst device.
In the first aspect of the invention, the catalyst device may include a partition wall formed by porous material and divides the inside of the catalyst device into a plurality of axial spaces, and a flow amount control portion that is arranged at at least one of an upstream end and an downstream end of the axial space and controls a flow amount of the exhaust gas.
In the above aspect of the invention, the flow amount control portion may be arranged at the upstream end or the downstream end of the partition wall which surrounds one of two adjacent axial spaces.
In the above aspect of the invention, the flow amount control portion may be a plug which is arranged at one of the upstream side and the downstream side of each axial apace and prevents the exhaust gas from flowing.
In the above aspect of the invention, the flow amount control portion may be a tapered portion which enlarges or reduces an opening area of the axial space.
In the above aspect of the invention, the tapered portion may be provided with a passage which has a cross section area smaller than a cross section area of the axial space.
In the above aspect of the invention, the tapered portion may be formed by deformation of the partition wall.
In the above aspect of the invention, the flow amount control portion may be a catalyst coating layer that carries a catalyst on the partition wall.
In the first aspect of the invention, both of the particulate filter and the catalyst device may be arranged in a housing.
In the first aspect of the invention, the catalyst device may be positioned around the particulate filter.